<!DOCTYPE html>
<html>
<head>
<!-- Tests that `opacity` causes a new stacking context to be formed. -->
<style>
section {
    position: absolute;
    width: 100px;
    height: 100px;
}

#a {
    background: red;
    top: 0;
    left: 0;
    z-index: 2;
}

#b {
    background: #00ff00;
    top: 25px;
    left: 25px;
    z-index: 1;
    opacity: 0.5;
}

#c {
    background: blue;
    top: 50px;
    left: 50px;
    z-index: 3;
}

#container {
    width: 200px;
    height: 200px;
}
</style>
</head>
<body>
<section id=a></section>
<section id=c></section>
<div id=container>
    <section id=b></section>
</div>
</body>
</html>

